Steps to reproduce:
1. Create a project with versions A, B, C, D, and E (or 1, 2, 3, 4, 5, etc), A being the first version and E being the last.
2. Create a six issues, the first with fix version as A, the second as B, and so on, then one with the fix version as A and E.
3. In the Issue Navigator, run the following JQL query: fixVersion >= "B" AND fixVersion <= "D"
The issues with fix version B, C, and D are returned.
The issues with fix versions B, C, and D are indeed returned, but so is the issue with fix versions A and E.
The same issue occurs if you use just < and > instead of >= and <=.